Any decent chromer will do an OPC , just decide how much polishing you want done . I recently had some pre stamp old Sugino's done , asked the chromer not to over polish because I still wanted the cast marks visible . Some chromers could over polish them smooth & IMO make them look worse than before , bit like over polished welds or when some ally stuff is polished within an inch of it's life .
Where are you based ? , best to find local chromer & go see them and explain what you want done ( look at Yell.com etc for chromers local to you ) .